In the manufacturing of various devices or parts, such as an engine block or a head for the engine block, the part is predrilled and tapped to provide threaded holes for bolts for securing the part to another part. For example, threaded holes are drilled and tapped in the engine block so that the head can be secured thereto. After the predrilling and tapping operations, it is desirable to check each of the tapped holes to determine if the hole exists at all, whether the hole has been drilled to the proper depth, and whether or not the hole has been properly tapped.
Various devices have been proposed to perform these operations. These devices typically include a probe having a fluid outlet and means for sensing the pressure of air passed through the fluid outlet. The probe is inserted into the hole and the sensor detects increased back pressure within the probe caused by the absence of threads in the hole, or the sensor detects a predetermined collapsing movement of the probe indicative of the lack of a hole or the presence of a hole of insufficient depth.
None of these prior art devices have achieved widespread commercial acceptance since they have been incapable of adjustment or calibration to suit the particulars of various work environments or, if calibration is provided, the calibration has proven to be very awkward and commercially impractical. Further, the various signals provided by the prior art devices have proven to be of limited usability in a commercial environment.